1. Field of the Invention
The present invention relates to a light emitting device, and more particularly, to a light emitting device having a light extraction structure, which is capable of achieving an enhancement in light extraction efficiency and reliability, and a method for manufacturing the same.
2. Discussion of the Related Art
Light emitting diodes (LEDs) are well known as a semiconductor light emitting device which converts current to light, to emit light. Since a red LED using GaAsP compound semiconductor was commercially available in 1962, it has been used, together with a GaP:N-based green LED, as a light source in electronic apparatuses, for image display.
The wavelength of light emitted from such an LED depends on the semiconductor material used to fabricate the LED. This is because the wavelength of the emitted light depends on the band gap of the semiconductor material representing energy difference between valence-band electrons and conduction-band electrons.
Gallium nitride (GaN) compound semiconductor has been highlighted in the field of high-power electronic devices because it exhibits a high thermal stability and a wide band gap of 0.8 to 6.2 eV.
One of the reasons why a GaN compound semiconductor has been highlighted is that it is possible to fabricate a semiconductor layer capable of emitting green, blue, or white light, using GaN in combination with other elements, for example, indium (In), aluminum (Al), etc.
That is, it is possible to adjust the wavelength of light to be emitted, using GaN in combination with other appropriate elements. In other words, where GaN is used, it is possible to appropriately determine the material of the LCD in accordance with the characteristics of the apparatus to which the LCD is applied. For example, it is possible to fabricate a blue LED useful for optical recording or a white LED to replace a glow lamp.
By virtue of the above-mentioned advantages of the GaN-based material, techniques associated with GaN-based electro-optic devices have rapidly developed since the GaN based LEDs became commercially available in 1994.
The brightness or output of an LED manufactured using the above-mentioned GaN-based material mainly depends on the structure of an active layer, the extraction efficiency associated with external extraction of light, the size of the LED chip, the kind and angle of a mold used to assemble a lamp package, the fluorescent material used, etc.